Research on Green Environmental Adhesives (2)

Since then, the author has seen another report: after years of research on social epidemics, the Tianjin Institute for the Study of Liver Diseases found that many young people in our country have fatty liver due to drinking, which will slowly lead to cirrhosis and finally to liver cancer. Therefore, regular heavy drinking can damage your health.
In addition, from the toxicity description in the “Solvent Manual”, it can be seen that compared with alcohol and ethyl acetate, ethyl alcohol is more powerful than ethyl acetate in terms of the extensiveness and seriousness of damage to human organs. Excerpts are as follows:

1. Ethanol (ie alcohol). In addition to damage to the central nervous system and reflexes of the paralyzed movement, it can also cause gastritis, indigestion, chronic liver disease and cirrhosis, and even pancreatic and heart disease.

2. Ethyl acetate. Anesthetic effect, its vapor stimulation eye, skin and mucous membranes, high concentrations of steam can cause liver and kidney congestion, a large number of sustained inhalation, acute pulmonary edema can occur.

It can be seen that although alcohol has not been found to have carcinogenic properties more than a decade ago, it is known that it has damage to the stomach, liver, pancreas and heart, while ethyl acetate only stimulates the eyes, skin and mucous membranes. In high-concentration atmospheres, it is only congested and paralyzed. Acute pulmonary edema can only occur when a large amount of vapor is continuously inhaled. The organs affected by ethyl acetate are not only less than ethanol, but also are temporary acute clinical manifestations. After a period of disengagement, the symptoms will disappear and the body will be able to recover without permanent damage like ethanol. . Therefore, the toxicity of alcohol to the human body is stronger than that of ethyl acetate, but the previous understanding of it is not completely deep or impenetrable!

Because the odor of alcohol is better than ethyl acetate, it is usually said to be “wine”. The human body does not reject its instinct, stays in an environment with high alcohol content, and does not leave actively, often resulting in prolonged exposure and large amounts of Inhalation. However, ethyl acetate has a pungent odor and the human body has an instinct to reject it. It is impossible to resist long-term, large-scale exposure to or inhalation of its vapor. Therefore, at this level, the chances of ethyl acetate harming the human body are lower than those of alcohol, and the degree of harm will be reduced.

In order to understand the mechanism of the poisoning of alcohol to human health and the extent of poisoning, the United States has long established the National Institute for Alcohol Abuse and Alcoholism, and set up the National Institute of Health to set up an alcohol research institute. Fourteen research centers invest more than 400 million U.S. dollars a year to study the damage caused by alcohol to human health. In November last year, the “Nutrient Science Research Institute” under the “Shanghai Institute of Biological Sciences” of the Chinese Academy of Sciences established a new “Alcohol Research Center” and hired Li Dingkai, director of the National Institute for Alcohol Abuse and Alcoholism, as an advisor. In order to find out the effect of alcohol on the liver disease of the 140 million hepatitis B patients in our country, we must consider the study of alcohol on national health. All these indicate that both the United States and China have attached great importance to the study of the issue of alcohol on human health and the degree of environmental impact. At present, we can say that alcohol is non-toxic, green, and environmentally friendly, and that alcohol-soluble inks and alcohol-soluble adhesives are hygienic, safe, and non-toxic, and that they are green. I am afraid that it is not appropriate or is too early to say that ethyl acetate is a solvent. Polyurethane adhesives are toxic, they are not green, they are not environmentally friendly, and their basis is insufficient.

Water-soluble or water-dispersible polyurethane adhesives, similar to the case of aqueous polyacrylate adhesives, replace water with ethyl acetate and ethanol. There are undoubtedly more advantages for solvent media, but if you consider To the end-capping agents, emulsifiers, stabilizers, pH regulators and cold-resistant antifreeze agents, they still do not know how much damage they have to human health. From the viewpoint that all products that are harmful to the human body cannot be called green, the author believes that water-based polyurethane adhesives cannot be compared with ester-soluble polyurethane adhesives or solvent-free adhesives that do not use these additives at all. Agents are seen as truly green products.

Therefore, the author believes that when it comes to truly hygienic and environmentally friendly adhesives, there is no need for a solvent-based polyurethane adhesive.

Solvent-free polyurethane adhesives are available in one-component and two-component formulations.

One-component solvent-free polyurethane adhesives and one-component solvent-based polyurethane adhesives are materials of the same molecular structure, all of which are polyisocyanate groups (ie, -NCO) and have a certain size. Molecular weight polymer:

H O O H
| ‖ ‖ |
OCN-RNCO-(～～～～)nOCNR-NCO
|
R
|
NCO
One-component solvent-free polyurethane adhesives are cured by moisture vapour cross-linking. Under normal circumstances, at least one of the substrates to be composited is a material with a high water vapor transmission rate, such as paper or fabric, or a large amount of water is retained on the surface of the substrate or quantitatively humidified (ie, sprayed) during compounding. Steam) so that the isocyanate groups in the glue can be cross-linked and cured. However, when using such an adhesive, the amount of humidification is difficult to control and the quality of the product is difficult to grasp. Therefore, similar to the dry-type compounding method, the most commonly used is a two-component non-solvent type polyurethane adhesive, and the one-component type is rarely used.

The two-component solvent-free polyurethane adhesive, like the solvent-based two-component polyurethane adhesive, is divided into two components, a main agent and a curing agent. When used, the main agent and the curing agent are mixed in a quantitative ratio, fully stirred and evenly coated, and then coated on the first base film. Without heating and drying, the base compound can be compounded directly with another base film. It is based on the active hydrogen in the main agent reacted with the isocyanate group in the curing agent to achieve the requirement of cross-link curing. This cross-linked curing is an "addition polymerization" chemical reaction, unlike the "condensation polymerization" reaction, which releases by-products of low molecular weight (such as water or carbon dioxide, etc.), and the composite product does not have defects such as air bubbles or white spots. The quality is high and easy to control and stable.

After nearly 40 years of development, high-quality, two-component, solvent-free polyurethane adhesives have been commercialized, including common plastic/plastic composites, aluminum/plastic composites, water-resistant cooking, and cooking-resistant types. The combined operating temperature also varies from the first generation of 80 to 90°C to the second generation of 60 to 70°C to the third generation of 40 to 50°C, and increasingly closer to room temperature, which is the use of The people provided convenience and were very popular.

Since the solvent-free polyurethane adhesive completely abandons any kind of solvent, it is a 100% effective substance and has the highest resource utilization rate. It conforms to the requirements of a scientific, scientific, and sustainable development concept that requires no energy consumption. Dry, energy consumption is much less than water-based and solvent-based adhesives, and the cost of solvent-free composite equipment is lower than that of dry or wet composite equipment, and the footprint of the equipment is small, and the overall investment can be reduced by about 20%. First, its production rate is more than three times higher than that of dry compounding, and the output rate is extremely high. In addition, the amount of dry-base rubber is smaller than that of water-based or solvent-based compound, and the entire solvent-free composite production cost is lower than Water-based or solvent-based dry compounding, at least 40% to 50%.

In addition, non-solvent polyurethane adhesives do not contain many additives like water-based or alcohol-soluble ones. All ingredients are known, comply with US FDA § 175.105 and China's GB9685 "food containers, packaging materials. The substances specified in the Hygiene Standards for use of adjuvants do not contain any additives or additives that are toxic or harmful to the human body. Like the ester-soluble polyurethane adhesives, they are completely safe, safe, reliable, and can be completely eliminated. Residual solvents and additives, no odor and toxicity, especially with the successful development and application of energy-crosslinking curing type solvent-free polyurethane adhesive, it can be achieved in a few seconds under the effect of ultraviolet rays or electron beams. The purpose of the curing, after the machine can be immediately cut into bags, then you can fill the contents and allow to undergo pasteurization, boiling or even high-temperature cooking sterilization, greatly reducing the delivery time, improve labor productivity, economy The benefits are very significant.

The non-solvent adhesive and its process method for producing composite packaging materials have endless advantages. In all the current varieties, the author believes that it is the most compatible with hygienic and environmental protection. Application and development research should be vigorously promoted.

Although today's solvent-free adhesives are not yet able to fully catch the quality of ester-soluble polyurethane adhesives, for example, they are still not resistant to high temperature cooking above 130°C, and they have not yet been resistant to media, especially aggressive media (such as organic solvents). Strong acid and alkali, liquid pesticides, etc.) However, with the development of research, its varieties will continue to increase, the quality will be improved, the field of application will continue to expand, and eventually will be on an equal footing with ester-soluble polyurethane adhesive, Keeping pace, even at some point, solvent-free adhesives can substantially replace other types of adhesives, and most compound packaging products can be produced using a solvent-free compounding process.

Source: Global Flexible Packaging Industry